In the field of disc brakes sensor units for wear detection with different embodiments are known.
From EP 0 492 143, for example, it is known to detect the wear of the brake linings at the end of an adjustment spindle facing away from the brake disc, in that the rotation of the adjustment spindle, which correlates with the translational movement compensating the wear-induced clearance or slack, is utilized as a measure. A similar method has been described in EP 0 566 006.
DE 43 12 377 discloses a sensor device in which the displacement movement of the brake actuation mechanism in the brake caliper is preferably detected by a linear potentiometer.
From EP 0 784 162 a wear monitoring device is known in which the movement of a thrust spindle is detected by means of a gear. For that purpose the thrust spindle comprises a gear rack which meshes with a gear pinion of a sensor unit.
From WO 2004/111484 of the applicant it is known to linearly sense the movement of the thrust spindle at the face surface of the thrust spindle facing away from brake disc.
It is common to all solutions of the prior art that these cannot ensure an exact wear sensing, since always the tolerances in the brake actuation mechanism and vibrations and tensions in the brake caliper do influence the measuring result and thus do negatively affect the accuracy.